1. Field of the Disclosure
The present disclosure relates to a semiconductor device, and more particularly, a nitride semiconductor light-emitting device.
2. Discussion of the Related Art
A nitride semiconductor light-emitting device includes ultraviolet, blue, and green light-emitting regions. Specifically, a GaN-based nitride semiconductor light-emitting device can be applied to an optical device of red/green light-emitting diode (LED), and an electronic device corresponding a high-speed switching or high-power device of MESFET (Metal Semiconductor Field Effect Transistor) or HEMT (Hetero Junction Field-Effect Transistor).
FIG. 1 is a cross section view illustrating a nitride semiconductor light-emitting device according to the related art.
As shown in FIG. 1, the nitride semiconductor light-emitting device according to the related art includes a substrate 110, a buffer layer 120, an undoped semiconductor layer 130, an N-type nitride semiconductor layer 140, an active layer 150, a P-type nitride semiconductor layer 160, a transparent electrode layer 170, a P-type electrode on the transparent electrode layer 170, and an N-type electrode 190 on the N-type nitride semiconductor layer 140 exposed by etching the active layer 150 and a predetermined portion of the P-type nitride semiconductor layer 160.
As a voltage is applied to the P-type electrode 180 and N-type electrode 190 in the semiconductor light-emitting device 100, a forward bias is applied between the P-type nitride semiconductor layer 160 and N-type nitride semiconductor layer 140, whereby electrons and holes are recombined in the active layer 150, to thereby emit light.
An important issue in the nitride semiconductor light-emitting device is how effectively the light generated in the active layer 150 is extracted to the external. In case of the nitride semiconductor light-emitting device according to the related art, as shown in FIG. 2A, a refractive index of a composing material of the nitride semiconductor light-emitting device is larger than a refractive index of an ambient material (for example, air, resin, substrate, and etc.) in the vicinity of the nitride semiconductor light-emitting device. Thus, photons generated inside the nitride semiconductor light-emitting device are totally reflected, and are then re-absorbed into the inside of the nitride semiconductor light-emitting device without escaping from the nitride semiconductor light-emitting device, thereby lowering light extraction efficiency.
In order to overcome this problem, there has been proposed a method for forming a stacking-structure wall with a predetermined angle in the semiconductor light-emitting device according to the related art, to thereby extract some of the transverse light generated in the active layer 150. However, this method causes the complicated manufacturing process of the semiconductor light-emitting device, and the increase of manufacturing cost.
In addition, the semiconductor light-emitting device according to the related art is problematic in that a dislocation density of nitride-based semiconductor layer grown on the substrate is raised due to a stress caused by a difference of lattice constant between the substrate and the nitride-based semiconductor layer grown on the substrate.